Method and system for starting a combustion engine

ABSTRACT

A method for starting a combustion engine fitted to a hybrid or dual-mode motor vehicle includes starting an additional motor upon a setpoint torque demanded by a driver of the vehicle, with a view to accelerating the vehicle beyond a threshold speed at which the combustion engine is driven beyond a stalling speed threshold when the combustion engine is mechanically coupled to wheels of the vehicle.

The present invention relates to the field of combustion engines ofvehicles provided with the function of automatically stopping andstarting said engines.

The invention relates more particularly to a method for starting acombustion engine fitted to a motor vehicle of the hybrid or dual-modetype and a system for implementing such a method.

The invention further relates to a motor vehicle of the hybrid ordual-mode type comprising such a system for starting a combustionengine.

In the prior art, it is known to provide vehicles with the function ofstopping and starting, also called “stop & start” or even “stop & go”,consisting of automatically shutting down the combustion engine when thevehicle is stationary, whilst respecting certain conditions (neutralposition, in particular with the parking brake engaged).

For example, in city driving when stopping at a red light the combustionengine is automatically stopped and then when the light turns to greenit is started up following an action or series of actions by the driver,indicating a desire to restart the vehicle.

Such a stopping and starting function aims to reduce the overallconsumption of the vehicle and to limit the polluting gas emissionsgenerated by this vehicle, in addition to noise pollution.

To achieve this, the vehicles are able to function according to the“stop & go” or “stop & start” mode, by the use of a reversibleelectrical machine, such as an alternator-starter which is coupled tothe combustion engine and powered by an inverter in start-up mode.

However, one of the major drawbacks associated with the use of analternator-starter is that it remains an extremely costly solution interms of manufacture and integration in a power train.

The present invention aims to remedy these problems resulting from thedrawbacks of the prior art, within the context of a vehicle comprisingtwo types of motor: a combustion engine motor and an additional motor ofthe electrical type or energy accumulation type.

Advantageously, the invention is implemented within a hybrid power trainwhich does not contain an alternator-starter and comprises a combustionengine and one or two electric motors.

The invention relates to a method for starting a combustion enginefitted to a hybrid or dual-mode motor vehicle, providing a starting ofan additional motor upon a setpoint torque demanded by a driver of thevehicle, with a view to accelerating the vehicle beyond a thresholdspeed at which the combustion engine is driven beyond its stalling speedthreshold when said combustion engine is mechanically coupled to thewheels of the vehicle.

In further embodiments:

-   -   the method comprises a processing step in which the speed of the        vehicle is compared to the threshold speed;    -   the starting of the combustion engine is carried out        simultaneously with the stopping of the additional motor when        the speed of the vehicle is substantially greater than or equal        to the threshold speed;    -   the coupling of the combustion engine to the wheels of the        vehicle is carried out by the closure of a clutch of the        vehicle;    -   the method comprises a torque switching step, providing that the        starting of the combustion engine and the stopping of the        additional motor are carried out such that the torque provided        to the wheels by the additional motor reduces as the torque        provided to the wheels by the combustion engine increases;    -   the method comprises a step of configuring the combustion        engine, permitting the starting thereof;    -   the step of configuring consists in the activation of a device        for supplying fuel to the combustion engine and/or a device for        the spark ignition of the vehicle and/or a device for preheating        a mixing chamber of the combustion engine, and    -   during the coupling, the method provides a determination of a        suitable gear ratio which permits the continuity of the setpoint        torque demanded by the driver of the vehicle to be ensured.

The invention further relates to a system for starting a combustionengine fitted to a hybrid or dual-mode motor vehicle, comprisinghardware and software elements implementing a method for starting acombustion engine as claimed in any one of the preceding claims.

Advantageously, the hardware elements comprise a control unit, a speedsensor, an additional motor and a coupling device, the coupling devicecomprising, in particular, a robot-controlled gear box and a clutch andbeing capable of connecting the combustion engine to the wheels of thevehicle by means of a transmission chain.

The invention further relates to a hybrid or dual-mode motor vehiclecomprising a combustion engine, the vehicle comprising such a startingsystem of the combustion engine, in particular the combustion engine andthe additional motor being connected to different axles.

Further advantages and features of the invention will become moreapparent from reading the following description of a preferredembodiment, with reference to the figures below, provided by way ofindicative and non-limiting example:

FIG. 1 shows schematically a vehicle comprising a system for controllingthe starting of a combustion engine according to this embodiment of theinvention;

FIG. 2A shows the speed of the vehicle relative to the time, within thecontext of implementing the method for starting the combustion engineaccording to this embodiment of the invention;

FIG. 2B shows the torque provided by the combustion engine relative tothe time, within the context of implementing the method for starting thecombustion engine according to this embodiment of the invention;

FIG. 2C shows the torque provided by an additional motor relative to thetime, within the context of implementing the method for starting thecombustion engine according to this embodiment of the invention, and

FIG. 3 illustrates a switching between the torques provided by thecombustion engine and the additional motor, within the context ofimplementing the method for starting the combustion engine according tothis embodiment of the invention.

In a non-limiting manner, this embodiment of the invention isimplemented inside a vehicle comprising a hybrid 1 or dual-mode powertrain.

Such a vehicle comprises a chassis, a front axle comprising a shaft 8connecting the front wheels 11, a rear axle comprising a shaft 9connecting the rear wheels 10.

The hybrid 1 or dual-mode power train comprises two different types ofmotor, one motor thereof corresponding to a combustion engine 2, and anelectric motor which thus corresponds to the additional motor 3 definedabove.

The electric motor 3 is connected to a high voltage battery by means ofa converter and an electronic control unit for the power supply thereof.

According to the embodiment shown, the combustion engine 2 drives thefront shaft 8 and thus the front wheels 11, whilst the electric motor 3drives the rear shaft 9 and thus the rear wheels 10. These two motorsare mechanically independent of one another.

The electric motor 3 is thus arranged in the region of the rear axle ofthe vehicle or even integrated in said axle.

According to a variant embodiment, two electric motors are used, eachbeing designed to drive one of the wheels 10 of the rear axle.

According to an additional variant embodiment, the additional motor 3corresponds to an additional motor fitted on the vehicle, as acomplement to the hybrid 1 or dual-mode power train.

Regarding the combustion engine 2, this engine may be arranged in theregion of the front axle of the vehicle.

Thus, in this embodiment, the four wheels of the vehicle are motorized,without the complication of the mechanical transmission between thefront and rear trains which could be encountered in certain vehicles.

According to the proposed embodiment, the electric motor 3 located inthe region of the rear axle between the wheels 10 of the vehicle ismechanically connected to the rear axle shaft 9 by a transmissionelement 12. This transmission element 12 is capable of providing atorque which is transmitted to the wheels 10 by means of the rear axleshaft 9 in order to move the vehicle forward.

The electric motor 3 may comprise a clutch which is arranged so as tocontrol the torque provided by the transmission element 12. This clutchmay then also provide slippage so that the second drive wheels 10 areable to rotate at different angular speeds.

The combustion engine 2 is mechanically connected to a coupling device 7by a transmission shaft 15, said device comprising a gear box 5connected to a clutch 4 by one or more connecting elements 22. A torqueconverter may also be used.

This combustion engine 2 is capable of providing a torque which may betransmitted to the wheels 11 in order to permit the displacement of thevehicle, via the transmission shaft 15 and a transmission chain 20. Thistransmission chain 20 comprises the shaft 8 of the front axle, the frontwheels 11 being connected thereto, and the input transmission shaft 13and output transmission shaft 14 of the gear box 5.

Advantageously, according to a preferred embodiment of the invention,the gear box 5 is a robot-controlled gear box, capable of modifying thegear reduction ratio between the input transmission shaft 13 and theoutput transmission shaft 14 by hydraulic or electromechanicalactuators. Such a gear box is easier to control in the hybrid operatingmode of the vehicle, as well as at the start-up according to theinvention, than a manual gear box.

The vehicle also comprises a system for starting the combustion engine 2comprising:

-   -   a control unit 6 for controlling the operating mode of the        vehicle, connected to the motors 2 and 3 by a control connection        16 and connected to the coupling device 7 by means of the        connection 21. The control unit 6 also comprises hardware        resources which are capable of implementing a computer program,    -   at least one sensor 24 capable of providing information about        the setpoint torque provided by the driver or data        representative of this setpoint and transmitted by a connection        25 to the control unit 6. This information may comprise, in        particular, the activation of the accelerator pedal and/or brake        of the vehicle, in addition to the extent to which these pedals        are depressed;    -   at least one speed sensor 19 of the vehicle connected to the        control unit 6 by a connecting element 23.

The control unit 6 is, in particular, capable of determining dynamicallythe torques to be applied to each of the two front 8 and rear 9 axleshafts and optimizing the operation of the power train 1, also accordingto the motor functions 17 demanded by the driver and the drivingconditions 18, data which are also transmitted to the control unit 6.

As has been seen above, the vehicle comprises a power train 1 whichconsists of two different motors and which is able to function accordingto two modes: a purely electric mode where only the motor 3 permits thedisplacement of the vehicle and a hybrid mode where the control unit 6determines, as a function of the driving conditions, of the speed and ofthe torques required, which type of motor is most suitable from thecombustion engine motor and/or the electric motor.

In hybrid operation, when the vehicle moves, the control unit 6continuously receives signals from the speed sensor 19, from the sensor24, permitting the setpoint torque provided by the driver to bedetermined, in addition to the driving conditions 18 and the motorfunctions 17 desired by the driver. This setpoint torque corresponds,for example, to parameters resulting from the behavior of the driver.

This control unit 6 is also capable of monitoring the combustion engine2 and the additional motor 3 in addition to the coupling device 7 byreceiving/emitting signals from/toward each of said devices.

According to the invention, in hybrid mode, when the combustion engine 2is stopped by the stop & start device, when the driver wishes todisplace the vehicle once again, it is not the combustion engine 2 whichis started but the electric motor 3, with reference to FIGS. 2A and 2C.The vehicle is thus in an electric mode where the electric motor 3 aloneensures the displacement of the vehicle.

This mode continues as long as the speed of the vehicle is less than orequal to the speed V_(A). This speed V_(A) corresponds to a thresholdspeed at which the combustion engine 2 may be driven beyond its stallingspeed threshold, when the mechanical coupling is carried out. The valueof this threshold depends on the staging of the gear box and is between15 km/h and 40 km/h.

During a processing step, the control unit 6 thus compares the speed Vof the vehicle to the threshold V_(A), in order to determine if thecombustion engine 2 is able to be started.

When the speed V of the vehicle is substantially greater than or equalto the speed V_(A), at the time t_(a), the control unit 6 then emits asignal which aims simultaneously to start the combustion engine 2 and totrigger the stopping of the electric motor 3, with reference to FIGS.2A, 2B and 2C.

The control unit 6 also emits a signal to the coupling device 7 suchthat the combustion engine 2 is coupled to the wheels 11 of the frontaxle of the vehicle, by closing the clutch, during a coupling step.

More specifically, the transmission element 15 is mechanically coupledto the transmission chain 20 which connects this transmission element 15to the wheels 11.

During this coupling step, the torque provided by the combustion engine2 is controlled to be at zero, so that the driver does not feel a suddenjerk.

The control unit 6 also implements a configuration of the combustionengine 2 so that said combustion engine is ready to start up. To achievethis, the control unit activates a device for supplying fuel to thecombustion engine 2 and possibly a device for spark ignition of thevehicle—a controlled or electronic spark ignition system—or a device forpreheating the mixing chamber of the combustion engine 2.

During this coupling step, the control unit 6 also determines theappropriate gear ratio which will be applied by the coupling device 7via the gear box 5 in order to ensure the continuity of the torquedemanded by the driver.

Moreover, during a torque switching step, the control unit 6 providesthat the starting of the combustion engine 2, at the time t_(a), and thestopping of the additional motor 3 are carried out such that the torqueprovided to the wheels 10 by the additional motor 3 reduces until itbecomes zero, at the time t_(b), as the torque provided to the wheels 11by the combustion engine 2 increases.

This torque switching step is illustrated in FIG. 3 between the timest_(a) and t_(b) as defined above. This switching step permits acontinuity of torque in phase to be ensured, in particular with thesetpoint torque demanded by the driver.

After carrying out the switching step, from the time t_(b) the vehicletravels in hybrid mode with, according to the example proposed, only thecombustion engine 2 activated.

The hybrid mode may also comprise a simultaneous operation of theelectric motor 3 and the combustion engine 2 during, for example, veryrapid acceleration.

According to one embodiment of the invention, when the driver wishes todecelerate the vehicle, for example by lifting the foot from theaccelerator, the vehicle decelerates and the torque of the combustionengine 2 reduces as FIG. 2B shows.

Henceforth, from the time t_(c) when the torque generated by thecombustion engine is zero, the electric motor 3 is activated, producinga braking action which may be recuperative in order to transform a partof the mechanical energy as a result of the braking action intoelectrical energy. The additional motor 3 thus functions as a generator.This effect increases gradually as the speed reduces.

With reference to FIGS. 2A and 3, when the speed V of the vehicle issubstantially less than or equal to a threshold speed V_(E), less thanV_(A), the control unit 6 then emits a signal with the purpose ofstopping the combustion engine 2 and at the same time increasing theaction of the electric motor 3 in its operation as a generator.

The speed V_(E) corresponds to a speed threshold which is able to beconfigured in terms of the speed V of the vehicle being compared duringa processing step carried out by the control unit 6 in order todetermine if the combustion engine 2 has to be stopped. The value ofthis threshold speed V_(E) depends on the staging of the gear box andmay range from approximately 6 km/h to 12 km/h.

The control unit 6 also emits a signal to the coupling device 7 suchthat the transmission element 15 of the combustion engine 2 ismechanically decoupled from the transmission chain 20 which connectsthis transmission element 15 to the first wheels 11 of the front axle ofthe vehicle.

In a variant embodiment of the invention, it may be provided that thecontrol unit 6 takes account of the battery charge for controlling thestarting mode of the vehicle, as conceived in the present invention. Itis conceivable, in particular, that the control unit 6 inhibits thisoperating mode when the level of battery charge is low and/or ensuresthat a device permits the battery to be recharged in the driving phasesof the vehicle so that the vehicle may be started by the additionalmotor.

It should be noted that in one variant the combustion engine 2 and theadditional motor 3 may be connected to the same axle.

This additional motor 3 may also relate to any motor operating accordingto the following technologies:

-   -   fuel cell;    -   latent energy from the compression-expansion of gas, and/or    -   flywheel.

1-11. (canceled)
 12. A method for starting a combustion engine fitted toa hybrid or dual-mode motor vehicle, comprising: starting an additionalmotor upon a setpoint torque demanded by a driver of the vehicle, with aview to accelerating the vehicle beyond a threshold speed at which thecombustion engine is driven beyond a stalling speed threshold when saidcombustion engine is mechanically coupled to wheels of the vehicle. 13.The method as claimed in claim 12, further comprising comparing a speedof the vehicle to the threshold speed.
 14. The method as claimed inclaim 12, wherein the starting of the combustion engine is carried outsimultaneously with a stopping of the additional motor when a speed ofthe vehicle is substantially greater than or equal to the thresholdspeed.
 15. The method as claimed in claim 12, wherein the coupling ofthe combustion engine to the wheels of the vehicle is carried out by aclosure of a clutch of the vehicle.
 16. The method as claimed in claim14, further comprising a torque switching step, providing that thestarting of the combustion engine and the stopping of the additionalmotor are carried out such that a torque provided to the wheels by theadditional motor reduces as a torque provided to the wheels by thecombustion engine increases.
 17. The method as claimed in claim 12,further comprising configuring the combustion engine, permitting thestarting thereof.
 18. The method as claimed in claim 17, wherein thestep of configuring includes activating a device for supplying fuel tothe combustion engine and/or a device for a spark ignition of thevehicle and/or a device for preheating a mixing chamber of thecombustion engine.
 19. The method as claimed in claim 12, wherein duringthe coupling, the method includes providing a determination of asuitable gear ratio which permits continuity of the setpoint torquedemanded by the driver of the vehicle to be ensured.
 20. A system forstarting a combustion engine fitted to a hybrid or dual-mode motorvehicle, comprising: hardware and software elements configured to startan additional motor upon a setpoint torque demanded by a driver of thevehicle, with a view to accelerating the vehicle beyond a thresholdspeed at which the combustion engine is driven beyond a stalling speedthreshold when said combustion engine is mechanically coupled to wheelsof the vehicle.
 21. The system as claimed in claim 20, wherein thehardware elements comprise a control unit, a speed sensor, theadditional motor, and a coupling device, the coupling device comprising,a robot-controlled gear box and a clutch and being configured to connectthe combustion engine to the wheels of the vehicle by a transmissionchain.
 22. A hybrid or dual-mode motor vehicle, comprising: a combustionengine including the system as claimed in claim 20, wherein thecombustion engine and the additional motor are connected to differentaxles.